Amek Mozart Neve EQ Topology

[krabbencutter]

I recently acquired an AMEK Mozart MZ 15 RN Channel Strip, which is one of the AMEK modules that were designed by Rupert Neve. Does anybody know which topology the EQ is using for the mid bands? The schematics can be found here https://www.audioschematics.dk/media/schematics/consoles/AmekMozartMZ15-RN-Input-module-schems.pdf (p. 45) and I have also attached a working Spice simulation.
It seems to be a pretty flexible proportional-Q design with variable frequency & Q and to my delight it also uses standard potentiometers. I'd love to learn more about it, but I currently don't know what to google for. So if anyone could maybe point me in the right direction, that would be great

 

[Ricardus]

I can't speak to the question, but I worked at a studio that had a 40 ch Mozart, and the first 24 channels were the RN cards, and the rest were Graham Langley. When it was working it was a good sounding desk to mix on. The center section was needlessly complicated, but the mixes were fat.

 

[My3gger]

I worked on Amek Mozart and another with some RN modules, material for repairs was ordered from Audio Maintenance. They needed replacement of some switches, pots, the rest was fine. Manual, older posts here, Audio Maintenance if they still sell those parts/mods, will provide needed information.
We had great times with those mixers recording to tape

 

[Ricardus]

I wonder if it would be possible to do the RN EQ on a 500 series module.

 

[krabbencutter]

I wonder if it would be possible to do the RN EQ on a 500 series module.

I'm thinking about modifying it, to bring it closer to the discontinued Portico 5033

 

[Ricardus]

I'm thinking about modifying it, to bring it closer to the discontinued Portico 5033

For 500 series? I'd love to see that. If you need a panel designed let me know.

 

[krabbencutter]

The service manual mentions biquad sections for the EQ, so I did some digging and it seems to be some sort of state variable biquad filter as described here https://www.analog.com/en/technical-articles/a-beginners-guide-to-filter-topologies.html (Fig. 4). I've rearranged the simulation layout to make the filter topology more clear.

 

[porkyc]

On the usual in-line console, the EQ is either in the monitor or the channel path.
The RN version had a "split" facility, whereby the top/bottom could be in one path and the 2 mids in the other. Can't remember (or CBA'd) as to which was which.
Thus the EQ had to be designed to accommodate wide ranges into both paths and thus failed trying to be all things to all men.
The bog standard arrangement of the Graham Langley SVF in one path or the other is much better.

 

[Ricardus]

On the usual in-line console, the EQ is either in the monitor or the channel path.
The RN version had a "split" facility, whereby the top/bottom could be in one path and the 2 mids in the other. Can't remember (or CBA'd) as to which was which.
Thus the EQ had to be designed to accommodate wide ranges into both paths and thus failed trying to be all things to all men.
The bog standard arrangement of the Graham Langley SVF in one path or the other is much better.

I worked on a Mozart that had 24 RN channel cards and something like 16 Langley cards, and from what I remember, the EQ on the RN cards had a little arrow button that would move the entire EQ to either the short throw input faders, or the long throw tape return faders.

The Amek console where you could move mids (at least that I worked on) was the "Big." It had a button on the EQ called "Mids to channel" and that would move both midrange channels to the input pot. And the "Big" was a Langley design.

 

[SIXTYNINER]

.... also 9098 pre+eq on 500 shape (plate paint, knobs, etc.. included)
would be very good ,
and maybe it would sound better than the Mozart RN ?

let's leave the word about to the experts.

cheers

 

[Ricardus]

.... also 9098 pre+eq on 500 shape (plate paint, knobs, etc.. included)
would be very good ,
and maybe it would sound better than the Mozart RN ?

There's a repair company in NY City that I used to deal with called E.A.R.S. Expert Audio Repair Service, and some years ago they got ahold of a bunch on Mozart RN channel cards, and racked up the Preamp/EQ section in a 2U rack, and sold them. I remember discussing the project with them because they were a client of the company I worked for, and we were providing the signal I/O harnesses to them for this project. He told me something about removing anything that had to do with the console automation from the cards improving the sound of the finished Preamp/EQ.

Anyway, just a 20 year old memory.

 

[L´Andratté]

A little hard to follow the switching on the schematic but isn´t this a standard SVF derived eq?

 

[SIXTYNINER]

.......... He told me something about removing anything that had to do with the console automation from the cards improving the sound of the finished Preamp/EQ.

VCA bypass ?

 

[Ricardus]

VCA bypass ?

Sure. I mean the VCAs aren't needed for a racked up preamp/EQ module, but I feel like there was more to it than that. I'm sure if you reached out to Jeff he would remember.

 

[porkyc]

A little hard to follow the switching on the schematic but isn´t this a standard SVF derived eq?

Yes! So if you start with that in mind, it's easier to work out the schematic given that it's a 4-in-a-line SVF sidechain topology.

 

[porkyc]

I worked on a Mozart that had 24 RN channel cards and something like 16 Langley cards, and from what I remember, the EQ on the RN cards had a little arrow button that would move the entire EQ to either the short throw input faders, or the long throw tape return faders.

The Amek console where you could move mids (at least that I worked on) was the "Big." It had a button on the EQ called "Mids to channel" and that would move both midrange channels to the input pot. And the "Big" was a Langley design.

This from the Mozart RN documentation out there:-
"The Equaliser stage can be switched between the channel and monitor paths in two blocks of the HF and LF sections and/or the two MF sections."

This apparently is a good idea, some salesman would tell you. ie a gimmick. The idea being that both paths had a "reasonable" EQ.
Hence either the Graham Langley 2500/2520 or the RN 9098 eqs are better as a single 4-band unit, because the individual ranges are more controlled. If you take the range ratio per band beyond 20:1, the HF end of any band gets very compressed. (see Douglas Self). ie not much use.

 

[Matt Syson]

I have been commissioning or repairing Mozarts since 1999 when around the 3rd or 4th was delivered and find it interesting to see the internet frothing over a load of things people don't understand.
It is the value of some components and the exact layout of the circuit tracks that really differentiate between 'rival manufacturers gear. AMEK made around 20 or more different desks over the years and although there were some common sections of circuitry used (with a small handful of variations) it is more the layout and 'facilities' offered that were the differentiators. Having a VCA in the signal path (the automation when engaged) adds a small amount of 2nd harmonic (warmth) depending on whether it is trimmed optimally for the level your signals are running at. Distortion depends on both level and frequency so a 'sweet spot' can be almost anywhere. Being able to split an EQ so parts can be used in 2 paths simultaneously CAN be an advantage if you are wanting to tame some frequencies when recording (room resonance) for which some might prefer filters with variable frequency and slope but you have to stop messing around sometime. Desk panel colour and layout of controls is also a significant factor whether people 'like' a specific desk or not, in the same way you may prefer your car over others because the ash tray is in a better position (if you are a smoker).
For what it is worth a pair of Mozart MX11 channel strips sound 'different' to a mZ12 (stereo strip) although the circuits are the same, same components assembled by the same ladies and of course the frequency responses are the same. It is the 'crosstalk' within the strip that causes the difference which is not normally appreciated or spotted when using usual methods of testing. Crosstalk being the same signal but pre or post other parts of it's own signal path (or adjacent channel path).

 

[porkyc]

Matt, my cynicism towards the gimmick split EQ is from having been, like you, involved with in-line consoles for a very long time; I don't see the MozRN advantage of this "feature". Split filters, Yes. Being able to use the hi-pass in the channel for recording and the EQ in the monitor path (this SSL introduced) is a good thing. The MCI guys (when Sony) copied this on the MXP3000.
If you need EQs in both paths, then use a grouping style console (and never sit in the control room's sweet spot).

Back to the original question, it is now apparent it's a standard 4-way SVF circuit.
My point is that if you are going to copy/rip off somebody else's intellectual property, rip off a decent one!! (Mentioned earlier).
And if you do want very wide ranging bands, then you have to think about switching cap values out/in to get a x3 function to avoid the upper frequency range compression. (And therefore get a more delicate/accurate frequency positioning).
Also, to understand the SVF tuned circuits used in the MozRN, look at BP's Net EQ; they are the same, using linear pots down to ground for the variable frequency component. If you hunt around the web, you will find a couple of parametric schematics that give the formula for the values.
BP's overall topology is different in that he has the SVFs all in parallel being steered into the 1st or 2nd pass amps for the ±, whereas the "standard" way is 4 inverting pass amps in series each with its own tuned circuit.

Also, for a good treatise on EQ series topology, not just the tuned circuits, dig out Walter Jung's book "Audio IC Op-Amp Applications" 3rd edition.
The M2500 is quite staightforward and at the time, none of the other console manufacturers were offering 4-band fully parametric for that price. And the schematic is easy to follow, it's not spread across how ever many pages, and on understanding it, (with the help of the above book) you will realise that the BP style SVF that you like (because it does not use dualRA pots) can be used instead.
The one thing that Rupert did was to have the HF first of the 4 in series, because everyone boosts top, so if you go for say, the M2500, reverse the order so it's HF, UpperM, LowerM, LF.
On the other hand, the NetEQ is so flexible it can be modified to suit most requirements; that's the whole point of it.
PC

 

[krabbencutter]

My point is that if you are going to copy/rip off somebody else's intellectual property, rip off a decent one!!

Might be because English is not my native language, but your comment sounds to me like you're telling me how to spend my spare time. I appreciate all the insight about the EQ tho!

 

[Ricardus]

Might be because English is not my native language, but your comment sounds to me like you're telling me how to spend my spare time. I appreciate all the insight about the EQ tho!

I would love to build some Mozart RN EQ clones if that's where you're going with this project.